U.S. Pat. No. 4,123,270, incorporated herein by reference, discloses a layered electrophotographic imaging element of high sensitivity which has been successfully used in commercial electrophotographic reproduction devices.
Typically, a layered photoconductor of this type comprises an electrically conductive supporting substrate, covered by a charge generating layer, this layer in turn being covered by a charge transport layer. The layered photoconductor may be rigid or flexible, as its supporting substrate is rigid or flexible. An exemplary flexible substrate is aluminized polyethylene terephthalate film. Typically, the aluminum surface of such a film is coated with an adhesive layer of a suitable material such as polyester resin, of which PE 200 brand by B. F. Goodrich Chemical Company is a specific example. This adhesive layer is then meniscus coated with a charge generating photoconductive layer. U.S. Pat. No. 4,123,270 describes a charge generating layer of an organic dye material selected from organic primary amine soluble charge generating monoazo and disazo compounds, and from organic primary amine soluble charge generating derivatives of squaric acid. Example 1 of this patent describes the use of chlorodiane blue (CDB) as the charge generating layer, whereas example 26 of this patent describes the use of hydroxy squarylium; 2-4-bis-(2-hydroxy-4-dimethylamino-phenyl)-1,3-cyclobutadiene-diylium-1,3- diolate; as the charge generating layer.
Copending and commonly assigned U.S. patent application Ser. No. 126,912, filed Mar. 3, 1980, now U.S. Pat. No. 4,307,167, in the name of L. D. Bowden et al, is also incorporated herein by reference. This patent describes the use of tetramethylbenzidine (TMB) as the charge generating layer of a layered photoconductor.
The final top layer of such a known layered imaging element is a charge transport layer. The p-type hydrazone containing charge transport layer of U.S. Pat. No. 4,150,987, incorporating herein by reference, is preferred. This patent is also of interest in that its example 6f suggests the use of polycarbonate as the aforementioned adhesive coating which coats the substrate's aluminum surface.
When a layered photoconductor is formulated in accordance with example 1 of U.S. Pat. No. 4,123,270, using the charge transport layer of U.S. Pat. No. 4,150,987, the result is a very acceptable electrophotographic imaging element of superior properties such as low light fatigue, low dark fatigue, low dark decay and acceptable sensitivity. However, the imaging element is not sensitive, to an acceptable degree, to the radiant energy output of a gallium arsenide laser.
The advent of so-called laser printers, which utilize electrophotographic reproduction devices, makes such sensitivity a desirable feature of an imaging element. The spectral output of a gallium arsenide laser is maximum at about 8200 angstroms.
A layered photoconductor in accordance with example 26 of U.S. Pat. No. 4,123,270 does in fact possess acceptable sensitivity to the output of such a laser. However, this photoconductor is not entirely acceptable in the areas of light fatigue, dark fatigue and dark decay.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawing.